The present invention relates to methods and apparatus for improved hydrocyclones, and particularly relates, in one non-limiting embodiment, to hydrocyclones having orifices that have been treated, coated or otherwise modified to have a surface that is more resistant to blockage or plugging than prior to the treatment, coating or modification.
Hydrocyclones are well known. They are devices to classify, separate or sort liquids and/or particles in a liquid mixture based on the densities of the liquids, or in suspension based on the densities of the particles. That is, a hydrocyclone may be used to separate solids from liquids or to separate liquids of different density. A hydrocyclone will normally have a cylindrical section at the top where liquid is fed tangentially and a conical base. The angle, and hence length of the conical section, plays a role in determining operating characteristics.
A hydrocyclone often has two exits on the axis in opposing directions: the larger on the underflow or accept and a smaller at the overflow or reject. In the context herein, the terms “reject” and “overflow” are used interchangeably. The underflow is generally the denser or thicker fraction, while the overflow is the lighter or more fluid fraction. The terms “reject” or “accept” tend to be value judgments on the worth of the respective exiting streams.
Internally, centrifugal forces are generated by the rapid acceleration of the fluids through the inlet ports of the hydrocyclone. Denser particles or fluids migrate towards the wall for eventual exit via the underflow, whilst the finer, or less dense particles and fluids migrate towards the core, remain in the liquid and exit at the overflow through a tube extending slightly into the body of the cyclone at the center or through a reject port.
Solid-liquid hydrocyclones and liquid-liquid hydrocyclones differ in some features. For instance, the diameter of the overflow or reject ports in liquid-liquid hydrocyclones tend to have relatively smaller diameters for a given cyclone body diameter. Additionally, the cone angles on solid-liquid hydrocyclones tend to be in excess of 20° included angle whereas for liquid-liquid hydrocyclones the included angle tends to be less than 5° or be a continuous acceleration geometry.
Liquid-liquid hydrocyclones commonly have a relatively small reject port, typically having an internal diameter of from about 1.5 to about 5 mm, through which the lighter phase fraction exits. The accumulation of foreign material or contaminants in this orifice over time causes constriction or plugging and this restriction or plugging restricts or inhibits the flow of the lighter phase leading to a reduction in hydrocyclone performance.
Normal operation would require these orifices to be “backflushed”, that is, to reverse the flow of fluid through the reject orifice, which process aims to use the differential hydraulic pressure to dislodge the obstructing material. In certain applications where the differential pressure is limited or the solids have a high affinity for the orifice surface, the backflushing is often not successful. Also, fluids pass through the path of least resistance, so if only one orifice of many is blocked, it becomes difficult to dislodge the foreign matter because the backflush fluids pass through the unblocked orifices.
It would be desirable if methods and apparatus were devised that could provide orifices that were less susceptible to blocking or plugging.